Creatine is, without a doubt, one of the most popular sports supplements of our time. Given how directly people associate it with improved performance and body composition you could even place it ahead of whey protein powder, which many athletes now seem to treat like a food—or, in some cases, a food group.

Part of creatine's appeal is, of course, due to its effectiveness. Most of the people who take it simply see greater strength, power, and muscle growth as a result, and the research backs this up. Creatine also happens to be one of the most studied supplements, both in a sports setting and in how it interacts with various medical conditions. In short, if you're not taking creatine because you're afraid of a certain side effect, that side effect has probably been looked at in a laboratory setting.

Want the straight truth about what creatine will or won't do to your heart, liver, or kidneys? Here's what the existing research has to say.

General Side Effects and Concerns

First off: Yes, creatine can cause water retention. This is probably no surprise. Regardless, unless you have a specific concern—like hypertension that requires treatment with diuretics—it's not a medical issue. For people concerned about looking bloated, the water retention happens in your muscles, so it actually makes you look a bit larger. This explains why some bodybuilders cut out creatine near the end of their contest prep. The rest of us needn't worry.

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Regarding other potential side effects:

Stomach distress. This can happen when you take too much creatine at once, perhaps during a loading phase, without much else in your stomach. The remedy is usually simple: either increase your water and food intake when you take creatine or just take smaller doses of creatine throughout the day.

Intestinal distress or diarrhea. This also can happen when you simply take too much creatine in a single dose. Since it cannot be absorbed in high quantities, this can cause osmotic diarrhea, a condition where water gets drawn into the bowels. The solution, again, is to take smaller doses.

All of the common side effects associated with creatine stem from its absorption profile in the intestines. At low doses, around 1-3 grams, creatine is absorbed well. As the dose gets higher, the absorption decreases, which is why you can't overdose on creatine—at least, not in a way that would present a medical concern.

There are some claims that creatine can contribute to cardiovascular issues such as arrhythmia, but they seem to be based on anecdotes and the placebo effect.

What About The Liver?

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A common knock against creatine is that it's bad for the liver, but this doesn't withstand scrutiny. A number of human studies have looked specifically at creatine usage and liver parameters and found no association between the supplement and liver problems.1,2

If you really want to go cherry-picking, a single study found liver problems in a particular mouse strain after 300 days of supplementation.3 Even with that in mind, human studies done on people with amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's Disease, over a span of 9-16 months failed to find any problems with liver enzymes.4-6

What About The Kidneys?

The idea that creatine could cause kidney damage comes from the following logic:

One of the tests for a malfunctioning kidney is for creatinine. If the creatinine levels in your blood are high, your kidneys could be malfunctioning.

Creatinine is a waste product of creatine, and loading creatine will increase your creatinine levels.

Elevated creatinine levels in and of themselves aren't a problem. They can be indicative of kidney problems, but they can also occur independent of kidney problems. On some level, it's understandable that this caused someone to sound the alarm, but it doesn't make it a reason to avoid taking creatine.

Human studies on biomarkers of kidney function during creatine supplementation have shown no significant alterations in BUN (blood urea nitrogen) or urinary glucose or proteins, and GFR (glomerular filtration rate) also remained unaffected. This was shown in people with ALS,4-6 postmenopausal women,7 athletes,8 young adults,9-11 and type-2 diabetics.12 Even a dose of 2 grams was shown to be fine for dialysis patients over the course of four weeks.13

Rat studies on a model with two-thirds nephrectomy—literally removing 66 percent of the kidney—found no issues with creatine.14,15 There is also a case study of a man with a single kidney having no problems with 20 grams of creatine daily alongside his high-protein diet.16

One rat study did show harm in rats with polycystic kidney disease.17 What's more, a single human case study that noted an accelerated rate of kidney damage in a man with focal segmental glomerulosclerosis (FSG). The impairment stopped when the supplement was removed, and started again when reintroduced.18 Both of these conditions are characterized by kidney tissue edema, a swelling caused by water accumulating. It has been suggested that any kidney issues that cause edema could be made worse with creatine—or anything that causes water retention in this organ.

The Bottom Line

Looking at the current body of research, it's safe to say:

Creatine does not cause damage to skeletal muscle or the heart, liver, or kidneys.

Creatine, at this moment in time, seems to be fine for kidney disorders that are not characterized by edema and tissue swelling.

Based on limited research, it is probably wise to avoid creatine supplementation if you have polycystic kidney disease, focal segmental glomerulosclerosis, or another kidney disorder characterized by tissue swelling.

Creatine is one of the most commonly viewed topics on our website, Examine.com. We've pored over the research, and we see no reason to fear creatine (more creatine myths debunked). Modern athletes treat it like a vitamin, and with good reason: It's safe, healthy, cheap, and for most people, it simply works. Get some creatine monohydrate, take 5 g per day, and you're good to go. If only all nutrition was that simple!

Always consult with a qualified healthcare professional prior to beginning any diet or exercise program or taking any dietary supplement. The content on our website is for informational and educational purposes only and is not intended as medical advice or to replace a relationship with a qualified healthcare professional.